Heat treating furnace



Oct. 4, 1932. P. P. CIOFFI 1,380,806

HEAT TREATING FURNACE Filed April 10. 1931 /N VE N TOR R R C/OFF/ ATTOR/VEV Patented Oct. 4, 1932 UNlTED STATES PATENT OFFICE PAUL P.OIOFFI, OF BROOKLYN, NEW YORK, ASSIGNOR TO BELL TELEPHONE LABORA- ITORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK HEATTREATING FURNACE Application filed April 10,

treated in accordance with the methods described in said applicationsand other similar methods may be practiced more effectively on a largescale by a furnace especially designed for the purpose. A phase of thisheat treating problem involves, for example, the heating of magneticmaterials at temperatures around or above the melting point of iron;another phase is that of performing such heating in gases of controlledcomposition at controlled pressures; another phase is the provision ofapparatus capable of withstanding the pressures due to possibleexplosions in the case of accidental production of explosive mixtures;another phase is that of ready control and regulation of term peraturesand pressures with (if desired) suitable variation of them during theprogress of the treatment. By employing the furnace herein described thetemperatures, pressures and times of treatment may be selected andregulated in a convenient manner. A furnace of this kind is usefulespecially to treat materials of varying shape and/or compositioneconomically on a relatively large scale. It is suitable for heattreating magnetic materials at gas pressures approximating a vacuum upto 20 atmospheres at temperatures up to about 17 00 C.

To the extent that the present application discloses means for enablingthe practice on a commercial scale of the inventions described in thesaid prior applications, this application is to be read in the light ofthe former applications which are, by reference,

1931. Serial No. 529,021.

made a part of the present disclosure. However, the improved furnace maybe used to treat any desired. magnetic material or similar materials invarious gases at various temperatures and pressures.

A particular embodiment of this invention will now be described withreference to the accompanying drawing, in which Fig.1 shows a viewpartly in elevation and partly in section of a heat treating furnace ofthe electric resistance type embodying the principles of the invention;

Fig. 2 is a detailed view of a portion of the heating element of thefurnace; and

Fig. 3 is a detailed View of an insulating and pressure resistingbushing enabling the passage of electrical conductors through thefurnace walls.

In accordance with the drawing, a composite cylindrical heating element4 to be described in more detail hereinafter is contained in a furnacechamber constituted by a steel cylinder 5 of suitable wall thickness andinternal diameter. The element 4 is supported by an annular base 50having apertures 51 affording passages for gaseous atmospheres, as shownby the arrows. A steel head 6 provided with a water cooling chamber isbolted to the flange 7 so that circular knife-edged ridges protrudingfrom the lower surface of the head and upper surface of .the flange 7sink into a lead gasket 8 between them, thus insuring air and gas-tightjoints. A small thick plate glass window 9 in the head is provided forvisual observation and temperature measurements by means of an opticalpyrometer. Electrodes 15 are provided for establishing electricalconnection withthe heating element; they consist of threaded copper rods10 screwed into an insulating and pressure resisting sealing bushingwhich is shown in more detail in Fig. 3. In this bushing, a threadedinsulating plug 11 made of any suitable insulating material capable ofwithstanding heat and pressure is screwed into a cup-shaped threadedsteel plug 12 whose cup portion 13 is filled and 12, respectively, thesejoints are filled with a suitable sealing agent, such aslitharge-glycerine cement. Valves 17 and 18 are provided for controllingthe gas flow through the inlet and outlet pipes located at opposite endsof the heating element 4. The entire furnace structure is placed in avat 19 and cooled by a continuous stream of water entering through pipe20 and flowing out through pipe 21. The water level of the vat may, ifnecessary, be higher and cover the suitable metal.

terminals of the wires 10 which would then be insulated with water-proofinsulation.

The cylindrical heating element 4 consists of a threaded alundum tube 22(see Fig. 2) which is wound with heat resisting wires 23; two molybdenumwires in parallel have been found to be suitable. This Winding extendsover about three-fourths of the length of the heating element. At theupper and lower end of the heating element each wire of winding 23 isfastened to rods 25, which may be made of molybdenum, by passing thewire through openings in the rod and tying the wires together. (Only theconnection at the upper end is shown in detail in Fig. 2.) The rods 25are insulated from the metallic lugs 71 by being surrounded by a silicatubing 24; they are bound to the unthreaded portion of the alundum tubeby wires 70. The alundum tube thus constituted is surrounded by analundum shield 26. The tube and shield are connected to and centrallysupported by a thin external steel cylinder 27 which is fastened to twolugs 71, one at the top and one at the bottom of the heating element.The space between the steel cylinder 27, the alundum shield 26 and thelugs 71 may be packed with powdered alundum 30. If the furnace is usedonly as a vacuum furnace, the powdered alundum 30 may be omitted inorder to avoid evolution of'undesired gas by the alundum. The electricalconductor 28 is insulated with silica tubing 29. The entire heating unit4 may be readily removed from and inserted into the furnace chamber 5,for purposes of'inspection and repair, etc., by removing the cover6,detaching the copper braids 16 from the electrodes at 15, and liftingthe heating unit by its hooks 31 (by a chain hoist in the case of alarge furnace). The base 34 may consist of It may be integral with thebottom end of cylinder 5 or separate there from. When separate it mayconsist of any heat resistant material.

The mode of operation of an annealing treatment is as follows: The cover6 being removed from the furnace and the heating unit 4 being in theposition shown, the materials to be treated, which are preferablycontained in an annealing pot 53, are lowered into the heating unit 4and deposited upon the base 34; preferably also, the annealing pot 53has perforations 54, for the purpose of facilitating the circulation ofthe gaseous atmospheres around the materials. Then the cover is replacedand the bolts 55 tightened. The terminals 10 are connected to a suitableelectric circuit such as, for instance, any suitable power circuit,represented schematically by the source of current 40. The heat produced within the unit 4 by the dissipation of electric energy in itsWinding 23 may be controlled by adjustable resistance element 41. Thegases or gas mixtures in which it is desired to treat the magneticmaterials are admitted into and cleared from the furnace by pipes 32 and33 and their flow controlled by valves 17 and 18.

or vacuum or low pressure treatments, the inlet valve 17 must efiect ahermetic seal. The exhaust valve 18 is replaced with a connection to avacuum pump (not shown) to create a rarefied atmosphere or a vacuum ofany suitable degree within the air-tight furnace chamber.

The glass window 14 on top of the furnace permits visual inspection ofthe material under treatment, as well as measurement of the heattreating temperature by means of an optical pyrometer. ment 41 or othersuitable means may be employed to regulate the heat up to and beyond themelting point of the material under treatment in accordance with theindications of the pyrometerj Gas pressures greater and less than thosementioned herein may be applied in heat treating magnetic materials. Thewall thickness and/or the material of the exterior furnace chamber maybe modified in a manner appropriate to the pressures employed.

Whatis claimed is:

A furnace for heat treating'magnetic materials adapted to be operatedwhen contain ing hydrogenous atmospheres at pressures ranging from avacuum up to several atmospheres and at temperatures around the meltingpoint of iron, said furnace comprising a pressure resisting metallicshell having a removable hermetically sealing cover, a transparentpressure resisting window in said cover for visual and pyrometricobservation of the furnace interior, a hollow heating elementforreceiving the charge removably arranged in said shell and carryingelectric resistor wires, insulating and hermetically seal ing electricalinlets in said metallic shell for admitting electrode wires into thefurnace chamber, said inlets being gas-ti ht and provided with means toinsulatesaid wires from said shell, said means being of materialresistant to temperatures stated at the pressures stated. 7

.In witness whereof, I hereunto subscribe my name, this 8th day ofApril, 1931. I PAUL P. CIOFFI.

The resistance ele-

